PC World 1999 August/PCWorld_1999-08_cd.bin/doc/HOWTO/mini/NFS-Root-Client

Text File | 1999-02-08 | 16.9 KB | 354 lines

   NFS-Root-Client Mini-Howto
   [1]Ofer Maor, [2][e-mail]
   V4.1, 02 February 1999

   The purpose of this Mini-Howto is to explain how to create client root
   directories on a server that is using NFS Root mounted clients. You
   can find the latest version of this Howto (HTML or Text) at URL:
   [3]http://www.hcs.co.il/oferm/NFS-Root-Client/

   1. Copyright

   (c) 1996 Ofer Maor ([e-mail])

   Unless otherwise stated, Linux HOWTO documents are copyrighted by
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   as long as this copyright notice is retained on all copies. Commercial
   redistribution is allowed and encouraged; however, the author would
   like to be notified of any such distributions.

   All translations, derivative works, or aggregate works incorporating
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   may be granted under certain conditions; please contact the Linux
   HOWTO coordinator at the address given below.

   In short, we wish to promote dissemination of this information through
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   on the HOWTO documents, and would like to be notified of any plans to
   redistribute the HOWTOs.

   If you have questions, please contact Ofer Maor ([4][e-mail]),
   the author of this mini-HOWTO, or Greg Hankins, the Linux HOWTO
   coordinator, at [5][e-mail] via email, or at +1 404 853
   9989.

   If you have anything to add to this Mini-Howto, Please mail the author
   (Ofer Maor, [6][e-mail]
   ), with the information. Any new relevant information would be
   appreciated.

   1.1. Thanks

   I would like to express my thanks to the author of the NFS-Root Howto,
   Andreas Kostyrca ([7][e-mail]). His Mini-Howto helped
   me with the first steps in creating a NFS Root Mounted client. My
   Mini-Howto does not, in any way, try to replace his work, but to
   enhance it using my experiences in this process.

   I would also like to thank Mark Kushinsky ([8][e-mail]) for
   polishing the english and spelling of this Howto, thus making it much
   more readable.

   2. Preface

   This Mini-Howto was written in order to help people who want to use
   NFS Root mounting to create their client's directories. Please note
   that there are many ways to accomplish this, depending on your needs
   and intent. If the clients are individual, and each client has its own
   users and administrator, it will be necessary to make significant
   parts of the client dirs not shared with other clients. On the other
   hand if the client is intended for multiple users, and are all
   administrated by the same person (for instance, a computer class),
   make as many files as possible shareable in order to make
   administration more manageable. This Howto will focus on the second
   issue.

   2.1. General Overview

   When building a client's root directory, and trying to limit ourselves
   to the minimum client size, we mainly focus on which files can we
   share, or mount from the server. In this Howto I will recommend the
   configuration of a client based on my experience. But before we begin
   please note:

     * This Mini-Howto does not explain how to do the actual NFS Root
       mounting. Reffer to the NFS-Root Mini-Howto if you need more
       information about that issue.
     * I based most of my client's configuration on mounts and symbolic
       links. A lot of those symbolic links can be replaced by hardlinks.
       One should choose according to his personal preference. Putting a
       hardlink over a mount and a symbolic link has its advantages, but
       might cause confusion. A file will not be erased until all its
       hardlinks are removed. Thus, In order to prevent a case in which
       you upgrade a certain file, and the hardlinks still refer to the
       older version, you will have to be very careful and keep track of
       every link you put.
     * While mounting the information from the server, two concepts can
       be used. The first (most common) concept, is to mount the whole
       server root directory under a local directory, and then just
       change the path or link the relevant directories there. I
       personally dislike mounting root partitions of a server on
       clients. Thus, this Howto suggests a way to mount the relevant
       directories of the server to the relevant places on the system.
     * This Howto is based on my experience building client directories
       on a Slackware 3.1 based distribution. Things may be different
       (especially on the rc.* files), for other users, however the
       concepts should still remain the same.

   3. Creating the client's root directory

   3.1. Creating the directory tree

   First of all, you need to create the directory structure itself. I
   created all the clients under /clients/hostname and I will use it for
   my examples listed below. This, however, can be changed to anything
   else. The first stage, then, is to create the relevant directories in
   the root directory. You should create the following directories:
    bin, dev, etc, home, lib, mnt, proc, sbin, server, tmp, usr, var

   and any other directories you might want to have on your system.

   The local, proc, and dev directories will be used separately on each
   machine while the rest of the directories will be either party or
   completely shared with the rest of the clients.

   3.2. Creating the minimal file system needed for boot

   3.2.1. Creating the dev dir.

   Although the dev dir can be shared, it is better to create a separate
   one for each client. You can create your client's dev directory with
   the appropriate MAKEDEV scripts, however in most cases it is simpler
   just to copy it from the server:
    cp -a /dev /clients/hostname

   You should keep in mind that /dev/mouse, /dev/cdrom and /dev/modem are
   symbolic links to actually devices, and therefore you should be sure
   that they are linked correctly to fit the client's hardware.

   3.2.2. Copying the necessary binaries.

   Although we mount everything from the server, there is a minimum that
   we need to copy to each client. First of all, we need "init", our
   system will not be able to run anything before init'ing (as the author
   found out in the hard way ;-). So first, you should copy /sbin/init to
   your client's sbin dir and then so that rc.S will run, you should copy
   /bin/sh to the client's bin directory. Also, in order to mount
   everything you need to copy /sbin/mount to the client's sbin
   directory. This is the minimum, assuming the first line in your rc.S
   is mount -av. However, I recommend copying a few more files: update,
   ls, rm, cp and umount, so that you will have the basic tools in case
   the client has problems mounting. If you choose to leave your swap on
   line before mount, you should also copy the swapon binary.

   Since most of these binaries are by default dynamically linked, you
   will also need to copy a fair part of /lib:
    cp -a /lib/ld* /lib/libc.* /lib/libcursses.* /client/hostname/lib

   Hardlinking the binaries themselves, instead of copying them, should
   be considered. Please read my comments on this in part 2.1 of this
   Howto.

   Please notice, all of the information above assumes that the kernel
   has been given the network parameters while booting up. If you plan to
   use rarp or bootp, you will probably need the relevant binaries for
   these as well.

   Generally, you will need the minimum of files that will enable you to
   configure the network and run rc.S up to the point where it mounts the
   rest of the file system. Make sure you looked into your /etc/init and
   rc.S files, making sure there are no "surprises" in any of them, which
   will require other files to be accessed, before the first mount will
   take place. If you do, however, find such files, you can either copy
   them as well, or remove the relevant parts from your init and your
   rc.S files.

   3.2.3. The var directory

   The var directory, in most cases, should be separate for each client.
   However, a lot of the data can be shared. Create under the server
   directory a directory called var. We will mount the server's var
   directory there. To create the local var directory, simply type:
    cp -a /var /clients/hostname/

   Now, you have a choice as to what you want to separate, and what you
   want to share. Any directory/file that you want to share, simply
   remove it from the client's var dir, and symlink it to the
   /server/var/ directory. However please note that you should either
   symlink it to /server/var or to ../server/var but NOT to
   /clients/hostname/server/var as this will not work when the root
   changes.

   Generally, I would recommend separating /var/run, /var/lock,
   /var/spool, and /var/log.

   3.2.4. The rest of the directories

     * etc is explained thoroughly in the next section.
     * mnt and proc are for local purposes.
     * usr and home are merely mount points.
     * tmp is up to you. You can create a different tmp directory for
       each client, or create some /clients/tmp directories, and mount it
       for each client under /tmp. I would recommend that you provide
       each client with a separate tmp directory.

   3.3. Building the etc directory and configuring the clients

   Please Note - this section refers to building the etc directory which
   is mostly shared among the clients. If your diskless clients have
   separate system administrators, it's best to set up for each client a
   separate etc directory.

   3.3.1. Building a clients wide etc directory

   Although we separate the etc directories of the clients, we still want
   to share a large portion of the files there. Generally, I think
   sharing the etc files with the server's /etc is a bad idea, and
   therefore I recommend creating a /clients/etc directory, which will
   hold the information needed for the clients. To start with, simply
   copy the contents of the server's etc to the /clients/etc directory.

   You should add to this directory all of the non-machine-specific
   configuration files, for instance motd, issue, etc. and not the client
   specific ones.(i.e. inittab or fstab)

   The most important changes will be in your rc.d directory. First, you
   should change rc.inet1 to be suitable for your local setup. I pass all
   my network parameters to the kernel through the LILO/Loadlin,
   therefore I remove almost everything from rc.inet1 file. The only
   thing I leave there is the ifconfig and route of the localhost. If you
   use rarp or bootp, you will have to build it accordingly.

   Secondly, you should edit your rc.S. First, remove all the parts that
   are responsible for the fsck check as fsck will occur when the server
   boots up. Then, you should find the line that mounts your fstab. This
   should look something like:
    mount -avt nonfs

   The -t nonfs is there since normal clients first run rc.S and only
   later on use rc.inet1 to configure the Ethernet. As this will cause no
   NFS partitions to be mounted this line should be deleted. Therefore,
   change it to mount -av. If you need to run rarp/bootp to configure
   your network, do it in rc.S (or call the appropriate script from
   rc.S), before the mount, and make sure your physical bin and sbin
   directories have the necessary files available.

   After the mount -av is performed, you will have a working file system.
   Build a general fstab, so that you can later copy it to each client.
   Your fstab should look something like this:
    server:/clients/hostname    /               nfs     default  1 1
    server:/bin                 /bin            nfs     default  1 1
    server:/usr                 /usr            nfs     default  1 1
    server:/sbin                /sbin           nfs     default  1 1
    server:/home                /home           nfs     default  1 1
    server:/lib                 /lib            nfs     default  1 1
    server:/clients/etc         /server/etc     nfs     default  1 1
    server:/clients/var         /server/var     nfs     default  1 1
    none                        /proc           proc    default  1 1

   Please notice, that the keyword deafult might not work on all versions
   of mount. You might change it to rw or ro or remove all of the default
   1 1 part.

   Also, make sure your server's /etc/exports looks like this:
    /clients/hostname   hostname.domainname(rw,no_root_squash)
    /clients/etc        hostname.domainname(ro,no_root_squash)
    /clients/var        hostname.domainname(ro,no_root_squash)
    /usr                hostname.domainname(ro,no_root_squash)
    /sbin               hostname.domainname(ro,no_root_squash)
    /bin                hostname.domainname(ro,no_root_squash)
    /lib                hostname.domainname(ro,no_root_squash)
    /home               hostname.domainname(rw,no_root_squash)

   Other than the first line, which should be separate for each host, the
   rest of the lines can be replaced with a hostmask to fit all your
   hosts (like pc*.domain - keep in mind though, that * will substitue
   only strings without a dot in them). I suggest that you make most of
   the directories read only, but this is up to you. The no_root_squash
   will make sure root users on the clients have actual root permissions
   on the nfsd as well. Check out man exports(5). If you want users to be
   able to run passwd from the clients also, make sure the /etc has rw
   and not ro permissions. However, this is not advisable.

   Please note another thing concerning the rc.S file. In Slackware, by
   default, it creates a new /etc/issue and /etc/motd every time it runs.
   This function MUST be disabled if these files are mounted ro from the
   server, and I would recommend that they should be disabled in any
   case.

   Lastly, if you want to have the same userbase on the server as on the
   clients, you should choose between 1), using NIS (Yellow Pages - check
   the yp-howto), and then each client will have a separate /etc/passwd
   and /etc/group as it receives it from the NIS server. 2) In most
   cases, a simple symbolic link will suffice. Therefore, you will need
   to either hardlink /clients/etc/passwd to /etc/passwd, or if you
   prefer a symlink, link /etc/passwd to /clients/etc/passwd (and not the
   other way around, since the clients do not mount the server's etc
   directory). Do the same for /etc/group.

   3.3.2. Creating a client's etc directory

   Generally, most of the files in the client's etc should be symlinked
   to the /server/etc directory. However, some files are different for
   each machine, and some just have to be there when the kernel loads.
   The minimum you need from the etc dir is as follows:
    resolv.conf
    hosts
    inittab
    rc.d/rc.S
    fstab

   Since these 5 files can be identical on all clients, you can simply
   hardlink them or copy them again. However, with the rc.S and fstab
   file it is advised to keep a separate copy for each client. You will
   also need a separate etc/HOSTNAME for each client. I personally
   recommend having all of the rc.d files separate for each client, as
   configurationand hardware might vary from one to another.

   For each client, add to the fstab the proper swap line:
    /dev/swap_partition                 swap    swap    default  1 1

   The rest of the /etc files of the client, you can either hardlink to
   the /clients/etc/* files, or symlink them to the /server/etc (which is
   the mount point of /clients/etc/).

   Make sure your machine can resolve properly, either through a named or
   through etc/hosts. It is not a bad idea to keep the server's IP in the
   etc/hosts, instead of counting on resolving. If you will count only on
   named resolving, a problem in the named will prevent your clients from
   booting up.

   3.4. Booting Up

   Now, all you have to do is to boot up your machine, cross your fingers
   and hope everything works as it should :-).

   4. Creating more clients

   If you have followed my instructions so far this should be simple - cd
   to /clients/ and type:
    cp -a hostname1 hostname2

   and then make sure you check these points:

   rc.d/* files matches the hardware and wanted software configuration
   etc/HOSTNAME is correct, fstab's swap line is correct, the symbolic
   links of dev/mouse, dev/modem and dev/cdrom are right.

   Good Luck....

References

   1. http://www.hcs.co.il/oferm/
   2. mailto:[e-mail]
   3. http://www.hcs.co.il/oferm/NFS-Root-Client/
   4. mailto:[e-mail]
   5. mailto:[e-mail]
   6. mailto:[e-mail]
   7. mailto:[e-mail]
   8. mailto:[e-mail]